The present invention relates boardly to a boresight alignment apparatus, and in particular to an active boresight drift measurement and calibration apparatus.
The state of the art of boresight alignment apparatus is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,782,826 issued to Offutt on Jan. 1, 1974;
U.S. Pat. No. 3,926,523 issued to Chapman on Dec. 16, 1975;
U.S. Pat. No. 4,168,908 issued to Cubalchini on Sept. 25, 1979;
U.S. Pat. No. 4,227,807 issued to Pond et al on Oct. 14, 1980; 15 U.S. Pat. No. 4,627,722 issued to Falk et al on Dec. 9, 1986; and
U.S. Pat. No. 4,714,339 issued to Lau et al on Dec. 22, 1987.
Cubalchini discloses a pointing and tracking control system which adjusts the relationship between a source for producing an electromagnetic beam and a target. The patented device includes a retroreflector and a high efficiency diffraction grating.
Chapman discloses an optical system for angle measurement comprising four retroreflectors arranged in pairs. A laser beam is passed from the retroreflectors through a beam splitter to an interferometer. The angular displacement of the moveable retroreflectors is deduced from the distance between their ridges and the number of fringes generated at the beam splitter.
Pond et al discloses the interference effect of a pair of parallel beam changes in accordance with path length and object angle. The interference effect is summed at a detector, and then analyzed by a tracking circuit to determine object angle.
Offutt discloses an interferometer to measure changes in path length of an optical system due to changes in the angle of rotation of a rotatable device.
Folk et al discloses using interference fringes to obtain the three-dimensional coordinates of one or more distant point light sources.
Lau et al discloses a laser tracking system which senses the angular orientation of a target.
This design allows the accurate pointing of neutral beams over long ranges. The dominant error source for long range pointing is the boresight alignment drift between the beam direction sensor and the target tracker. A previous approach pointing is the boresight alignment drift between the beam direction sensor and the target tracker. A previous approach was to maintain thermal control of the structure connecting the two sensor boresights.
As target range increases beyond several hundred kilometers, structural thermal control alone becomes inadequate. This design reduces the need for increased thermal control for longer target ranges. Instead, boresight alignment drift is measured and then used for beam pointing compensation.
The active boresight drift alignment measurement and calibration apparatus may be utilized in applications in which various types of directed energy devices that require high pointing accuracy are needed. The apparatus uses separate light paths to spatially locate the relative position of each sensor element defining its boresight. As these lengths change by very small amounts, the resulting angular shift in boresights is geometrically computed.